Merge pull request #13 from CMEPW/feature/issue/12

Fixed a bug on old Python versions (< 3.8)

models.py

@@ -1,7 +1,7 @@
 import copy
 from abc import ABC
 from dataclasses import dataclass, fields, field
-from typing import List, Optional, Union, get_type_hints, get_args, get_origin
+from typing import List, Optional, Union, get_type_hints
 
 from dataclasses_json import dataclass_json
 from pydantic.typing import NoneType
@@ -11,6 +11,19 @@
 from utils.case import camel_case
 
 
+# HACK: This is a ugly fix for old Python versions
+import sys
+
+if sys.version_info < (3, 8):
+    def get_args(field):
+        return field.__args__
+
+    def get_origin(field):
+        return field.__origin__
+else:
+    from typing import get_args, get_origin
+
+
 def default_field(obj):
     return field(default_factory=lambda: copy.copy(obj))